The invention relates generally to hybrid and electric vehicles, and more specifically to systems and methods for operating power take-off systems aboard hybrid and electric vehicles.
Purely electric vehicles typically use stored electrical energy to power an electric motor, which propels the vehicle. Hybrid electric vehicles combine an internal combustion engine and an electric motor that is typically powered by one or more electrical energy storage devices. Such a combination may increase overall fuel efficiency by enabling the combustion engine and the electric motor to each operate in respective ranges of increased efficiency. It may be more efficient to use electric motors during startup, and use combustion engines primarily during sustained periods of constant engine operation. For example in a hybrid vehicle, having an electric motor to boost initial acceleration permits the use of a smaller and more fuel efficient combustion engine.
Some large conventionally-powered vehicles, such as trucks, tractors, and even marine craft, use power take-off (PTO) systems to provide power to an attached or separate machine. Typically, the PTO device draws power from the vehicle's combustion engine via a PTO shaft. Common applications for PTO systems include running water pumps on fire engines and marine vessels, running hydraulic pumps on trucks or other machinery, and running threshers and harvesters on agricultural vehicles. Other applications include raising/lowering a dump truck bed, operating the compactor on a garbage truck, operating a winch on a tow truck, or driving an electric generator.
Typically, mid and rear PTO shafts are provided on agricultural vehicles. Common PTO standards call for shaft rotation speeds of 540 or 1000 rpm, which is typically achieved by the mechanical coupling of the PTO shaft to the internal combustion engine through a clutch and gearbox arrangement. Normally, the engine must run at a fixed speed to provide the correct PTO shaft speed, which may result in reduced engine efficiency at partial load operation, or may limit the maximum torque or power that can be supplied by the PTO system. Further, running the engine at a speed that provides for the correct PTO shaft speed may constrain the ground speed of the vehicle. Additionally, mechanically coupling the PTO shaft to the engine via a clutch and gearbox arrangement may limit the number of locations where the PTO system can be employed.
It would therefore be desirable to design a PTO system configured to recapture energy from the PTO shaft during braking, wherein the engine speed is independent of the PTO shaft speed, and wherein the possible locations for placement of the PTO shaft is not limited by engine location as in some conventional vehicles.